US1821144A

US1821144A - Distillation process

Info

Publication number: US1821144A
Application number: US618772A
Authority: US
Inventors: John V E Dickson
Original assignee: Barrett Co Inc
Current assignee: Barrett Co Inc
Priority date: 1923-02-13
Filing date: 1923-02-13
Publication date: 1931-09-01
Anticipated expiration: 1948-09-01

Description

' spt. 1, 1931. J. v. E. DICKSON 1,821,144

DISTILLATION PROCESS Filed Feb. 15, 1923 anoemoz w, M W a.

Patented Sept. 1,1931

UNlTED' s'rn'rss PATENT OFFICE Joan v. n. mcxson, or wooncairr-on-nonson, new masnv, nssmnon we ran mamrconmm, a ooarona'rmn or new mnsmr DISTILL A'IION PROCESS Application filed February 18, 1928. Serial No. 618,772.

which is to be treated by the process described in this application will be referred to as tar and it will be understood that the term .coal .tar as used in the claims herein is intended to include coal tar as-well as coal tar m pitch obtained from the partial distillation of coal tar.

, It has been bound that if coal tars are distilled in such a way that they are exposed to unusually'hi htemperatures,durin distillation, or are eated at the usual dlstillation temperatures for unusually long periods of ,time, the total oil recoverable as distillate from them is less than usual, and also the residual pitch is of higher melting point than usual, after a given percentage of oil has been removed as distillate.

The oils'removed as distillate are almost always of higher commercial value than the residual pitches, and it is therefore desirable to carry out the distillation in such a way that either the maximum total yield of oil will be'attained, or the highest possible percentage of oil will be removed before any given commercial grade of pitch has been formed.

The use of tube stills, such for example as is disclosed on pages 485, 486, et seq. of the fifth edition, Part I, of Coal Tar and Ammonia, by Geo. Lunge, Ph. D., published by The D. Van Nostrand Company, 1916, wherein the tar is heated as it passes continuously through a series of tubes, and is finally (lischarged into a chamber where the oil vapors and pitch residue separate, has been found to increase the total removable distillate, and also to give a pitch residue of lower melting point on the removal of a'glven percentage of distillate, as compared with the use of the ordinary discontinuous method of distillation, where a charge of tar is heated to boiling and the various oil's pass over successively, in vaporform to a condenser. Since ap proximately the same temperatures are attained in both processes it is supposed that the difference in oil yields is due principally to the difference in the time during which the tar is heated, which is commonly about ten hours in the discontinuous method and less than one hour in the tube still.

Lowering the distillation temperatures, in the discontinuous method, by (a) carrying on the distillation under greatly reduced pressure mm. of mercury, absolute pressure, or less), or (b) the rapid passage through the tar of a gas having no chemical action on it, has been found to produce results practicalllly the same as those attained in the tube sti Accordingly, it might well have been sup posed that in any one of the three above methods (tube still, reduced pressure, or passage of gas) approximately the optimum conditions had been reached, with regard to the total oil yield attainable orthe oil yield attainable in the manufacture of any given pitch.

However, I have discovered that, in a tube still, (a) by a suificiently great further ro duction of the time during which the tar is heated, greatly increased yields of distillate oil can be obtained, in the production of a.

given commercial grade of pitch; (did (6) it, in addition to thus shortening the time, advantage be taken of the known boilingpoint-lowering efiect of reduced pressure (by artificially reducing the pressure in the separating chamber), a total yield of distillate can be obtained which is far in excess of that other improved methods amounts to the equivalent of 35-15% of the tar used.

These results are accomplished by heating the tar as it passes through one or more tubular paths or zones, and discharging it at substantially its maximum temperature into a chamber or zone of relatively large volume and correspondingly low pressure compared with said heating zone; where the oil vapors separate fromthe residual pitch, the vapors passing on into a condensing system and the pitch flowing out continuously at the bottom of the separating chamber. It is 1 important, however, that the time occupied by-the tar in traversing the heated tubes should be very short. Since it would be very difiicult to measure or to calculate the actual mean time taken by a particle of tar to traverse such an apparatus (because of the expansion due to rise of temperature, and the vaporization of oil taking place continuously during a considerable part of the travel), an indirect way of defining this length of time relatively must be used, and this will consist in defining the ratio of the cubic contents of the tubing traversed to the volume of the tar passing through it in unit time.

If the unit of volume be the cubic foot, and the unit of time be the minute, this ratio will indicate the mean time which would be occupied by a particle of tar in passing through such a piece of apparatus. This ratio for commercial tube stills is commonlyabout 60, but in the present invention it is not more than 10, and may be much less or in other words, the tar is passed through the heating tube or zone in amounts not less than onetenth of the cubical capacity of said heating tube or zone per minute.

In order to reduce the ratio to such low values, particular attention must be paid to the manner of supplying heat. A low value of this ratio means that a comparatively large quantity of tar is being heated per minute in an apparatus of comparatively small volume capacity; and this necessitates an in.- tense and concentrated application of heat. This invention is not limited to any particular method or means of supplying heat to the' tubing through which the tar fiows, but in the accompanying drawing is illustrated a form of apparatus, in which the heat may be supplied to the tubing by means of a bath of molten metal or alloy through which the tubing passes. The rapidity with which heat passes from a liquid to a metal in contact with it (as compared with the relatively slow passage of heat from a gas to a metal) permits a relatively large quantity of heat to pass per minute into the tube walls (and thence to the tar) without recourse to the very high temperatures in proximity to the tubes which would be necessary in order to transfer heat bath of molten metal or hot liquid metal, such as mercury, lead, or other metal of low melting point, in the tank 4. The metal in this tank may be kept in the molten state by heat,- ing the same in any convenient way as, for

example, by flames impinging upon the bot-F tom of the tank 4 or by passing hot products of combustion through pipes passing through tank 4. A pipe 5 leads from the coil 3 to a separator 6 for pitch and vapor which is provided with a baflle plate 7. The pitch settles 1 in the bottom of the separator 6 and passes through the pipe 8 into the pitch receiver 9, from which it may be withdrawn through the valve,10. The vaporized constituents pass. from the separator 6 through the pipe 11 into the coil 12 in the condenser 13 where they are condensed and passed to the oil receiver 14 from. whence the oil may be removed upwardly and is heated by the heat transmitted from the molten metal while it is in transit through the coil 3. The amount of heat supplied will be suflicient to cause the desired amount :of distillation to take place. The rate at which the tar is passed through coil 3 will be maintained as indicated above so as to produce an increased yield of oil or distillates in proportion to "the amount of pitch or. residue that is left.

The following are two examples out of many others that might be given to illustrate how the process has actually been carried out.

(1) A yield of distillate of 58% by weight with a pitch residue having a'melting point of 237 F. has been produced at atmospheric pressure in the separating chamber, with a discharging temperature of about 810 F., and a rate of tar flow of about 70% of the cubic capacity of the heating tube, per

' minute.

a rate of tar flow of about 38% of the cubic 125- capacity of the heating tube per minute, the separating chamber being maintained at an absolute pressure of 55 mm. of mercury.

In both of the above examples, a coke oven tar was used, which by ordinary distillation 1-30 gives about' 35% by weight of distillate in producing a pitch having a melting point of 237 F., and in an ordinary tube still or in the recirculated gas method gives about 46% in making a pitch of the same melting point. It is not practical to make a pitch having a melting point of' 352 F. by either the ordinary still or the ordinary tube still method because of danger of coking, but the highest yields customarily obtained from such a tar by these methods are about 40% by the former and 58% by the latter in making a pitch of melting point about 300 F.

claim: 1. The process of distilling coal tar which comprises passing said tar through a heated zone in amounts not less than one-tenth of the cubical capacity of said zone per minute, supplying heat to the tar while passing throughsaid zone at such a rate as to elevate it to a temperature sufiicient to cause about 58% at least of the tar to volatilize at atmospheric pressure, and then discharging the tar thus heated into a zone of relatively low pressure with respect to the pressure of said heated zone, thereby effecting a separation of the oil content in vapor form from the pitch content of the tar.

2. The process of distilling coal tar which comprises passing said tar through a heated zone in amounts not less than one-tenth of the cubical capacity of said zone per minute, supplying heat to the tar while passing through said zone at such a rate as to elevate it to a temperature of about 740810 F. prior to its discharge therefrom, and

' then discharging the tarthus heated to a zone of relatively low pressure with respect to the pressure of said heated zone, thereby effecting a separation of from about 58% to about 7 5% of the oil content in vapor form from the pitch content of the tar.

3. The process of distilling coal tar which comprises passing said tar through a heated zone in amounts not less than one-tenth of the cubical capacity of said zone per minute,- supplying heat to the tar while passing through said zone at such a rate as to elevate it to distillation temperature prior to its discharge therefrom and then discharging the tar thus heated into a zone maintained at a pressure less than atmospheric, thereby efiecting the separation of the oil content in vapor form from the pitch content of the tar.

4. In a process of distilling coal tar to recover volatile oils therefrom and produce a itch residue, wherein the tar is heated to.

istillation temperature while confined in and flowing through a heated zone and vaporization of the volatile oils is thereafter effected by discharging the heated tar into a chamber of low pressure relative to that of said heated zone, the improvement which comprises passing said tar through said heated zone at an increased rate of fiow amounting to not less than one-tenth of the cubical capacity of said zone per minute, and supplying heat to the tar while passing through said zone at a rate suflicient to elevate it to distillation temperature prior to its discharge therefrom, whereby the time period to which the tar is subjected to heat in its passage through the zone is diminished thereby lowering the extent'of thermal decomposition of the tar and increasin the oilyield, and recoverin separately t e volatile oil content of the tar libera'ted in the vaporization chamber and the residual itch.

5. In a process 0 distilling coal tar to recover volatile oils therefrom and produce a pitch residue, wherein the tar is heated to distillation temperature while confined in and flowing through a tube and vaporization of the volatile oils is thereafter effected by discharging the heated tar into a chamber of low pressure relative to that of said heating tube, the improvement which comprises passing said tar through said tube at an increased rate of flow amounting to not less than onetenth of the cubical capacity of said tube per 6. In a process of distilling coal tar to recover volatile oils therefrom and produce a pitch residue, wherein the tar is heated to distillation temperature while confined in and flowing through a tube and vaporization of the volatile oils is thereafter effected by discharging the heated tar into a chamber of low pressure relative to that of said heating tube, the improvement which comprises passin said tar through said tube at an increase rate of flow amounting to not less than one-third of the cubical capacity of said tube per ininute, and supplying heat to the tar while passing through said tube at a rate suflicient to elevate it to distillation temperature, prior to its discharge therefrom, whereby the time period to which the tar is sub'ected to heat in "its passage through the tu eis diminished thereby lowering the extent of thermal decomposition of the tar and increasing the oil yield, and recovering separately the volatile oil content of the tar recover volatile oils therefrom and produce a pitch residue, wherein the tar is heated to distillation temperature while confined in and flowing through a tube and vaporiza- 5 tion of the volatile oils is'thereafter efiected by discharging the heated tar into a chamber of low pressure relative to that of said heating tube, the improvement which comprises passing said tar through-said tube at an increased rate of flow amounting to approximately seven-tenths of the cubical capacity of said tube per minute, and supplying heat to the tar while passing through said tube at a rate suflicient to elevate it todistillation temperature prior to its discharge therefrom,

whereby the time period to whlch the tar is subjected to heat in its passage through the tube is diminished thereby lowering the extent of thermal decomposition of the tar and increasing the oil yield, and recovering separately the volatile oil content of the tar liberated in the vaporization chamber and the residual pitch.

In testimony whereof I aflix my signature.

'2'5 JOHN V. E. DIGKSO-N.